2126: Year of the comet

November 03, 1992

Scientists plodding away at the routine tedium of tabulating planetary positions stumble on impending Doomsday: A giant comet hurtling toward Earth. Frenzied calculations reveal the impact will occur in the not-too-distant future with sufficient force to wipe out civilization as we know it. Humanity can save itself, but only by banding together to avert common catastrophe.

Sound familiar? It should -- the killer asteroid from outer space is a classic scenario that has been told and retold in countless space adventure epics.

This time, however, the tale comes not from the hyperactive imagination of sci-fi writers, but from the staid International Astronomical Union. Last month, for the first time in its history, that august body issued an official warning of a potential collision between Earth and a speeding object swinging in from the fringes of the solar system.

The alarm, authored by Dr. Brian G. Marsden, director of the union's central bureau and associate director for planetary sciences at the Harvard-Smithsonian Center for Astrophysics, was buried in a one-page text on orbital computations for Comet Swift-Tuttle, an obscure interplanetary interloper that last appeared in 1862 and was rediscovered this year by a Japanese amateur astronomer.

Fortunately, Mr. Marsden says there is only about a one in 10,000 chance that the comet, which is several miles in diameter, will actually hit Earth. But if it did, he calculates the impact would occur on Aug. 14 in the year 2126, producing an explosion equivalent to a million Hiroshima-size bombs -- enough to disrupt Earth's climate and plunge its inhabitants into a new dark age.

That is why it is prudent to track the comet for as long as possible during its current pass through the inner solar system, as Dr. Marsden suggests. This will allow scientists to better determine the comet's orbit for the next pass and thus to help refine calculations of the odds of a collision.

Given 134 years' warning, humanity probably could mount an effective response if necessary. Mr. Marsden has suggested sending out a fleet of nuclear-tipped rockets to intercept the intruder and nudge it into a more benign orbit. By 2126 even more powerful techniques may have been developed. More worrisome, perhaps, is whether the fractious nations that share this planet could agree to cooperate against the common threat. That, more than any technological challenge, could well prove to be the limiting factor in humanity's ability to cope with the specter of cosmic annihilation.